The present invention relates to a micromechanical spring structure, in particular for a rotation rate sensor, having a first and a second cooperating elastic bar, segments of which run largely parallel to each other and segments of which are coupled with one another. Although it can be applied to any suitably appropriate micromechanical spring structure, the exemplary embodiments of the present invention are explained in reference to a micromechanical rotation rate sensor.
FIG. 4 shows a schematic top view of a micromechanical spring structure for a rotation rate sensor. In FIG. 4, reference number 10 designates a first elastic bar and 12 a second elastic bar. Reference number 15 is a connecting area in which first and second elastic bars 10, 12 are coupled with one another.
It is believed that such a micromechanical spring structure may have the disadvantage that, when sharp bends occur in connecting area 15, stress peaks may arise at the largely right-angle transitions between elastic bars 10, 12 and connecting area 15. In the worst case, this may result in cracks or complete destruction of connecting area 15.
An exemplary embodiment of the present invention concerns a particular design of the spring geometry. In particular, the first and second elastic bars have a common curved area in which they are coupled with one another by a connecting area. A first transitional area to the connecting area, located between the first and second elastic bars, forms a largely smooth curve. A curved area in this context means that either a curvature is constantly present in this area or a curve is produced here during operation.
It is believed that this type of geometry has the advantage that it may minimize or at least reduce stresses in the connecting area so that damage virtually cannot occur there or is at least limited.
According to another exemplary embodiment, the first and second elastic bars have a first widened area that merges with the first transitional area. It is believed that this has the advantage that it may further reduce any stresses that occur.
According to another exemplary embodiment, the first widened area narrows in a largely linear or trapezoidal manner as the distance from the first transitional area increases. It is believed that this may have the advantage of maintaining low stress values in the direction of operation and with respect to drop strength. The effect this can achieve is to distribute stresses and significantly reduce the stress maximum.
According to another exemplary embodiment, the first and second elastic bars are attached to a mainland area that is connected to a substrate, or to an island area that floats above the substrate. A second transitional area to the mainland area or the island area has a largely smooth curve. Smooth or smooth-curvature transitions in the attachment to the mainland and island, respectively, prevent stress peaks from occurring in these areas.
According to another exemplary embodiment, the first and second elastic bars have a second widened area that merges with the second transitional area. It is believed that this may have the advantage that it may further reduce any stresses that occur.
According to another exemplary embodiment, the second widened area narrows in a largely linear or trapezoidal manner as the distance from the transitional area increases. It is believed that this may have the advantage of maintaining low stress values in the direction of operation and with respect to drop strength.
According to another exemplary embodiment, at least one of the first and second elastic bars may have a circular third widened area that has a central attachment area for attachment to the substrate. It is believed that this may be an advantageous coupling method for suppressing natural frequencies while maintaining production safety during gas phase etching.
According to another exemplary embodiment, the first and second elastic bars have a double-U structure, and the connecting area is located in the double-U bend. It is believed that this structure has favorable symmetry. It is also believed that the double-U spring shape may be useful for providing two printed conductors of the same width that are insulated against one another on the elastic bars. It is also believed that the elastic bar structure of a single-U spring may have to be at least twice as wide, and thus at least twice as long, to achieve the same rigidity. The chip area is thus always much smaller when implementing a double-U spring. The two elastic bars are mechanically connected in the U-curve so that no acceleration components should arise orthogonally to the direction of vibration during resonant operation.
An acceleration component of this type would be active in the detection direction of a Coriolis rotation rate sensor that uses the spring structure and thus produce a quadrature, i.e., a spurious signal in the output voltage. In this exemplary embodiment, the connection is arranged to minimize or at least reduce any stresses occurring in the direction of movement and in the z-direction.
According to another exemplary embodiment, first and second printed conductor devices are attached to the first and second elastic bars for effectively insulating, i.e., separating, two printed conductors of equal width against one another.
According to another exemplary embodiment, the structure may be produced by silicon surface micromechanics or silicon surface micromechanics in conjunction with silicon bulk micromechanics, or a different micromechanical technology.